Steel pipe for water supply and preparation method thereof

Abstract

The invention relates to the technical field of steel pipes, and provides a steel pipe for water supply and a preparation method thereof. The steel pipe for water supply comprises a steel pipe body and an anti-corrosion layer arranged on the outer surface of the steel pipe body, and the anti-corrosion layer comprises a sintered epoxy layer, an adhesive layer and a polyethylene layer which are sequentially arranged from inside to outside; the polyethylene layer comprises the following raw material components in parts by mass: 90-110 parts of high-density polyethylene, 24-30 parts of composite kaolin, 4-8 parts of a lubricant and 1-3 parts of an antioxidant; the preparation method of the composite kaolin comprises the following steps: A1, adding kaolin and wollastonite into water, and uniformly mixing to obtain a mixed solution A; a2, adding acid into the mixed solution A to enable the pH value to be 3-4, and sanding to obtain a mixed solution B; and A3, adding acid into the mixed solution B to enable the pH value to be 1-2, sanding, filtering, washing and drying to obtain the composite kaolin. According to the technical scheme, the problem of poor ultraviolet aging resistance in the prior art is solved.

Description

Technical Field

[0001] The present invention relates to the technical field of steel pipes, and more specifically, to a steel pipe for water supply and a preparation method thereof. Background Art

[0002] Steel pipes for water supply are widely used in municipal water supply, industrial water conveyance and other fields due to their combination of the high strength of steel and the corrosion resistance of the polyethylene layer. However, its high-density polyethylene layer faces a severe aging problem in the long-term ultraviolet irradiation environment - the energy of ultraviolet rays will cause the molecular chains of high-density polyethylene to break and oxidize, resulting in the gradual embrittlement, cracking and even peeling of the polyethylene layer, and then losing the protective effect on the steel pipe. This problem is particularly prominent in areas with high ultraviolet intensity such as open storage of pipes, surface laying, high altitude, and tropical regions. It not only shortens the service life of the pipes, but also may cause safety hazards such as water leakage, increasing maintenance costs and environmental risks.

[0003] Currently, the conventional means in the industry to improve the ultraviolet resistance of the polyethylene layer include adding additives such as ultraviolet absorbers and hindered amine light stabilizers, but they generally have limitations: due to the easy migration and volatilization of small molecule additives during use, the protection effect is not ideal.

[0004] Therefore, it is of great significance to develop a steel pipe for water supply with improved ultraviolet aging resistance. Summary of the Invention

[0005] The present invention provides a steel pipe for water supply and a preparation method thereof, which solves the problem of poor ultraviolet aging resistance of the steel pipe for water supply in the related art.

[0006] The technical solution of the present invention is as follows: The present invention provides a steel pipe for water supply, comprising a steel pipe and an anti-corrosion layer provided on the outer surface of the steel pipe. The anti-corrosion layer comprises a fusion-bonded epoxy layer, an adhesive layer, and a polyethylene layer arranged in sequence from inside to outside; The raw materials of the polyethylene layer comprise the following components in parts by mass: 90 - 110 parts of high-density polyethylene, 24 - 30 parts of composite kaolin, 4 - 8 parts of lubricant, and 1 - 3 parts of antioxidant; The preparation method of the composite kaolin comprises the following steps: A1. Adding kaolin and wollastonite into water, mixing evenly to obtain a mixed solution A; A2. Adding acid to the mixed solution A to make the pH 3 - 4, and then sanding to obtain a mixed solution B; A3. Adding acid to the mixed solution B to make the pH 1 - 2, sanding, filtering, washing, and drying to obtain the composite kaolin.

[0007] In the present invention, in the polyethylene layer of the steel pipe for water supply, the use of a lubricant improves the processing performance of the polyethylene layer, thereby enhancing the quality of the final product. The good fluidity enables the polyethylene layer to cover the adhesive layer more evenly during the laying process, forming a polyethylene layer with uniform thickness and dense structure, ensuring the overall quality and protective performance of the polyethylene layer. At the same time, it reduces the adhesion between the material and the equipment, avoids defects in the polyethylene layer caused by local overheating or material accumulation, and further improves the stability and reliability of the polyethylene layer.

[0008] In the present invention, in the polyethylene layer of the steel pipe for water supply, the addition of an antioxidant ensures the antioxidant performance of the polyethylene layer, delays the aging rate of polyethylene during processing and use. During the high-temperature processing, the antioxidant can inhibit the oxidative degradation of polyethylene and maintain the stability of its physical properties. During the long-term use, the antioxidant continuously plays a role to prevent the performance deterioration of polyethylene caused by oxidation, such as the decrease in tensile strength and the reduction in flexibility, etc., and extends the service life of the steel pipe for water supply.

[0009] As a further technical solution, the mass-volume ratio of the kaolin to the water is 1 g: 10 - 12 mL.

[0010] As a further technical solution, in the anticorrosive layer, the raw materials of the fusion-bonded epoxy layer include the following components in parts by mass: 55 - 60 parts of epoxy resin, 22 - 30 parts of ethylene-vinyl acetate copolymer, 12 - 20 parts of petroleum resin, 18 - 30 parts of titanium hydride, 2 - 5 parts of benzoin, and 1 - 4 parts of adipic dihydrazide.

[0011] As a further technical solution, in the anticorrosive layer, the raw materials of the adhesive layer include the following components in parts by mass: 18 - 45 parts of ethylene acrylic resin, 7 - 14 parts of polyvinyl butyral, 8 - 20 parts of polyisobutylene, and 1 - 3 parts of dioctyl phthalate.

[0012] As a further technical solution, the mass ratio of the kaolin to the wollastonite is 10: 4 - 5.

[0013] In the present invention, the mass ratio of the kaolin to the wollastonite can be 10: 4, 10: 4.1, 10: 4.2, 10: 4.3, 10: 4.4, 10: 4.5, 10: 4.6, 10: 4.7, 10: 4.8, 10: 4.9, 10: 5, and preferably 10: 4.5.

[0014] In the present invention, in the composite kaolin of the polyethylene layer of the steel pipe for water supply, wollastonite is the key raw material that provides a silicon source for kaolin to form silica composite kaolin. Its mass ratio to kaolin directly affects the composite effect. When the mass ratio of kaolin to wollastonite is in the range of 10:4 to 5, wollastonite can provide sufficient and appropriate silicon source. In the subsequent sanding and acidification reaction processes, an appropriate amount of silicon source can ensure the formation of a uniform silica coating layer on the surface of kaolin. If the ratio of kaolin to wollastonite is lower than 10:4, the silicon source is insufficient, which may lead to incomplete coating of silica on the surface of kaolin, affecting the coating effect on kaolin and the final performance improvement in the polyethylene layer. On the contrary, if the ratio of kaolin to wollastonite is higher than 10:5, too much silicon source may cause the generated silica to agglomerate in the solution, not only unable to uniformly coat on the surface of kaolin, but also may form impurity phases in the polyethylene layer, damaging the microstructure of the polyethylene layer and having a negative impact on the performance of the steel pipe.

[0015] As a further technical solution, in step A2, during the sanding, the temperature is 20 - 30 °C and the time is 4 - 5 h.

[0016] As a further technical solution, in step A3, during the sanding, the temperature is 60 - 80 °C and the time is 2 - 3 h.

[0017] In step A2, when sanding, the temperature is controlled at 20 - 30 °C. This temperature range is relatively mild, which can not only ensure that the dissolution reaction of wollastonite in the acidic environment can proceed slowly and stably, but also will not cause the reaction to be too violent to control due to too high temperature. The time of 4 - 5 h ensures that wollastonite can be fully dissolved and in sufficient contact with kaolin under this temperature and acidic conditions. In step A3, when sanding, the temperature is raised to 60 - 80 °C. The higher temperature can accelerate the formation of a silica coating layer on the surface of kaolin more quickly. In this temperature range, the molecular thermal motion intensifies, the activity of silicate ions increases, and the collision frequency between them increases, which is conducive to the formation of a denser silica network structure. The time of 2 - 3 h ensures that the reaction of forming a silica coating layer on the surface of kaolin can proceed fully. During this period, as the reaction progresses, silica gradually deposits and grows on the surface of kaolin, forming a continuous, uniform and dense coating layer.

[0018] As a further technical solution, in steps A2 and A3, the acid is independently hydrochloric acid or nitric acid.

[0019] As a further technical solution, the concentration of the hydrochloric acid or nitric acid is 1 - 3 mol / L.

[0020] In the present invention, both hydrochloric acid and nitric acid are common and easily accessible chemicals in industry, with relatively low costs and wide sources, which helps to reduce the preparation cost of kaolin coated with silica. The concentration of the acid is controlled within 1 - 3 mol / L. Within this concentration range, it can not only ensure a suitable reaction rate between the acid and wollastonite but also ensure the controllability of the reaction. When the acid concentration is 1 mol / L, the hydrogen ion concentration is moderate, and the dissolution rate of wollastonite is relatively slow, but the reaction process is easy to control, which is conducive to the uniform release of silicon source and creates conditions for the formation of a uniform silica coating layer. As the acid concentration gradually increases to 3 mol / L, the hydrogen ion concentration increases, and the reaction rate accelerates, enabling wollastonite to be fully dissolved in a shorter time. When the concentration further increases, the problem of overly violent reaction will occur.

[0021] As a further technical solution, the composite kaolin is functionalized composite kaolin; The raw materials of the functionalized composite kaolin include composite kaolin and ethylene-methacrylic acid copolymer with a mass ratio of 10:0.5 - 1.

[0022] In the present invention, the molecular structure of ethylene-methacrylic acid copolymer lays the foundation for its role in enhancing the impact strength. In the ethylene-methacrylic acid copolymer molecule, the ethylene chain segment has a similar chemical structure and good compatibility with polyethylene, and can form a tight bond with the polyethylene matrix, thus improving the compatibility between the composite kaolin and polyethylene; moreover, the polar groups on the methacrylic acid chain segment can be connected to the polar groups on the surface of the composite kaolin through interaction. This unique structure enables the ethylene-methacrylic acid copolymer to build an efficient interfacial connection between the composite kaolin and polyethylene. When the water supply steel pipe is subjected to an impact load, the impact force first acts on the polyethylene layer. Due to the enhanced interfacial bonding force of the ethylene-methacrylic acid copolymer, the stress can be more effectively transferred from the polyethylene matrix to the composite kaolin particles. The composite kaolin particles have high strength and rigidity and can disperse the stress, avoiding stress concentration in the polyethylene matrix, thereby improving the ability of the polyethylene layer to resist impact damage and ultimately enhancing the impact strength of the water supply steel pipe.

[0023] As a further technical solution, the preparation method of the functionalized composite kaolin includes the following steps: Add the composite kaolin into xylene, mix evenly, add ethylene-methacrylic acid copolymer, stir, concentrate, and dry to obtain the functionalized composite kaolin.

[0024] As a further technical solution, the mass-volume ratio of the composite kaolin to the xylene is 1 g:7 - 8 mL.

[0025] As a further technical solution, during the stirring, the time is 3 to 4 h and the rotation speed is 200 to 300 rpm.

[0026] In the present invention, the temperature during the stirring can be any temperature that can ensure the complete dissolution of the ethylene-methacrylic acid copolymer.

[0027] As a further technical solution, the lubricant includes one or more of zinc stearate, calcium stearate, and polyethylene wax.

[0028] As a further technical solution, the antioxidant includes one or more of antioxidant 126, antioxidant 1076, and antioxidant 168.

[0029] The present invention also provides a method for preparing a steel pipe for water supply, which is used to prepare the steel pipe for water supply described above, and includes the following steps: S1. Blend, extrude, and pulverize the raw materials of the fusion-bonded epoxy layer to obtain epoxy layer powder; S2. Fusibly bond the epoxy layer powder to the outer surface of the steel pipe to obtain a fusion-bonded epoxy layer; S3. Blend, extrude, and pulverize the raw materials of the adhesive layer to obtain adhesive layer powder; lay the adhesive layer powder on the surface of the fusion-bonded epoxy layer to obtain an adhesive layer; S4. Mix and extrude the components of the polyethylene layer raw materials to obtain a polyethylene layer, lay the polyethylene layer on the adhesive layer, and apply pressure for compounding to obtain the steel pipe for water supply.

[0030] The working principle and beneficial effects of the present invention are as follows: The present invention uses silica - composite kaolin as the raw material for the polyethylene layer, improving the anti - ultraviolet aging property of the polyethylene layer. In the prior art, kaolin is often added to improve the strength of the polyethylene layer of steel pipes for water supply. However, since kaolin contains metal impurities such as iron, manganese, and copper, these metal ions will become catalysts for the photo - oxidation reaction under ultraviolet light irradiation, accelerating the aging of the polyethylene layer. In order to improve the ultraviolet - aging resistance of the polyethylene layer of steel pipes for water supply, the present invention uses composite kaolin, with silica compounded on the surface of kaolin. When ultraviolet light irradiates the anti - corrosion polyethylene layer of the steel pipe for water supply, silica is first used to absorb and scatter ultraviolet light, reducing the probability of contact between metal impurities in kaolin and ultraviolet light. At the same time, after silica is compounded on the surface of kaolin, due to the lamellar structure of kaolin and the different refractive indices of kaolin and silica for ultraviolet light, ultraviolet light will be blocked by the lamellar structure and affected by the refractive - index difference during propagation, resulting in reflection and scattering, making the propagation path of ultraviolet light in the polyethylene layer tortuous, further weakening the penetration ability of ultraviolet light to the polyethylene layer. Therefore, the present invention uses silica - composite kaolin as the raw material for the polyethylene layer of steel pipes for water supply, which acts together from the optical and physical levels, comprehensively improving the anti - ultraviolet aging performance of the polyethylene layer. In practical applications, the steel pipes for water supply prepared by the present invention are particularly suitable for steel pipes for water supply laid outdoors. Long - term exposure to sunlight, they can effectively resist ultraviolet erosion, greatly extend the service life of the polyethylene anti - corrosion layer, reduce problems such as pipeline corrosion and damage caused by ultraviolet aging, lower the maintenance cost, and ensure the long - term stable operation of the water supply system. Detailed Embodiments

[0031] The following will combine the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of the present invention.

[0032] In the following embodiments and comparative examples, the high - density polyethylene has the model of HE2550, the kaolin has a particle size of 3000 mesh, the wollastonite has a particle size of 1250 mesh, the ethylene - methacrylic acid copolymer has the model of Nucrel®0903, the epoxy resin has the model of SM601, the ethylene - vinyl acetate copolymer has the model of EVA910, the petroleum resin has the model of C9 petroleum resin, the ethylene acrylic resin has the model of EAA3440, the polyvinyl butyral has the model of B60H, and the polyisobutene has the model of HRD850.

[0033] Embodiment 1 A steel pipe for water supply includes a steel pipe and an anti - corrosion layer provided on the outer surface of the steel pipe. The anti - corrosion layer includes a fusion - bonded epoxy layer, an adhesive layer, and a polyethylene layer arranged in sequence from the inside to the outside; The raw materials of the fusion-bonded epoxy layer include the following components in parts by mass: 60 parts of epoxy resin, 30 parts of ethylene-vinyl acetate copolymer, 20 parts of petroleum resin, 30 parts of titanium hydride, 5 parts of benzoin, and 4 parts of adipic dihydrazide; The raw materials of the adhesive layer include the following components in parts by mass: 45 parts of ethylene acrylic resin, 14 parts of polyvinyl butyral, 20 parts of polyisobutylene, and 3 parts of dioctyl phthalate; The raw materials of the polyethylene layer include the following components in parts by mass: 110 parts of high-density polyethylene, 30 parts of composite kaolin, 4 parts of zinc stearate, 4 parts of calcium stearate, 1 part of antioxidant 126, 1 part of antioxidant 1076, and 1 part of antioxidant 168; A method for preparing composite kaolin includes the following steps: A1. Add kaolin and wollastonite into water (the mass ratio of kaolin to wollastonite is 10:7, and the mass-volume ratio of kaolin to water is 1 g:12 mL), mix evenly to obtain a mixed solution; A2. Add 3 mol / L hydrochloric acid to the mixed solution to make the pH 4, then grind it with sand at 30 °C for 4 h, then add 3 mol / L hydrochloric acid to make the pH 2, grind it with sand at 80 °C for 2 h, filter, wash, and dry to obtain composite kaolin; A method for preparing a steel pipe for water supply includes the following steps: S1. Blend the raw materials of the fusion-bonded epoxy layer, extrude, and pulverize to obtain epoxy layer powder; S2. Fusibly bond the epoxy layer powder onto the outer surface of the steel pipe to obtain a fusion-bonded epoxy layer; S3. Blend the raw materials of the adhesive layer, extrude, and pulverize to obtain adhesive layer powder; lay the adhesive layer powder on the surface of the fusion-bonded epoxy layer to obtain an adhesive layer; S4. Mix and extrude the components of the raw materials of the polyethylene layer to obtain a polyethylene layer, lay the polyethylene layer on the adhesive layer, and press and compound to obtain a steel pipe for water supply.

[0034] Example 2 A steel pipe for water supply includes a steel pipe and an anti-corrosion layer provided on the outer surface of the steel pipe. The anti-corrosion layer includes a fusion-bonded epoxy layer, an adhesive layer, and a polyethylene layer provided in sequence from the inside to the outside; The raw materials of the fusion-bonded epoxy layer include the following components in parts by mass: 55 parts of epoxy resin, 22 parts of ethylene-vinyl acetate copolymer, 12 parts of petroleum resin, 18 parts of titanium hydride, 2 parts of benzoin, and 1 part of adipic dihydrazide; The raw materials of the adhesive layer include the following components in parts by mass: 18 parts of ethylene acrylic resin, 7 parts of polyvinyl butyral, 8 parts of polyisobutylene, and 1 part of dioctyl phthalate; The raw materials of the polyethylene layer include the following components in parts by mass: 90 parts of high-density polyethylene, 24 parts of composite kaolin, 4 parts of calcium stearate, 1 part of antioxidant 1076; Preparation method of composite kaolin, comprising the following steps: A1. Add kaolin and wollastonite into water (the mass ratio of kaolin to wollastonite is 5:1, and the mass-volume ratio of kaolin to water is 1 g:10 mL), mix evenly to obtain a mixed solution; A2. Add 1 mol / L nitric acid to the mixed solution to make the pH 3, then grind it for 5 h at 20 °C, then add 1 mol / L nitric acid to make the pH 1, grind it for 3 h at 60 °C, filter, wash, and dry to obtain composite kaolin; Preparation method of steel pipe for water supply, comprising the following steps: S1. Blend the raw materials of the fusion-bonded epoxy layer, extrude, and pulverize to obtain epoxy layer powder; S2. Fusibly bond the epoxy layer powder on the outer surface of the steel pipe to obtain a fusion-bonded epoxy layer; S3. Blend the raw materials of the adhesive layer, extrude, and pulverize to obtain adhesive layer powder; Lay the adhesive layer powder on the surface of the fusion-bonded epoxy layer to obtain an adhesive layer; S4. Mix and extrude the components of the polyethylene layer raw materials to obtain a polyethylene layer, lay the polyethylene layer on the adhesive layer, and press and compound to obtain a steel pipe for water supply.

[0035] Example 3 A steel pipe for water supply, comprising a steel pipe and an anti-corrosion layer provided on the outer surface of the steel pipe, and the anti-corrosion layer includes a fusion-bonded epoxy layer, an adhesive layer, and a polyethylene layer provided in sequence from the inside to the outside; The raw materials of the fusion-bonded epoxy layer include the following components in parts by mass: 58 parts of epoxy resin, 26 parts of ethylene-vinyl acetate copolymer, 16 parts of petroleum resin, 22 parts of titanium hydride, 4 parts of benzoin, 2 parts of adipic dihydrazide; The raw materials of the adhesive layer include the following components in parts by mass: 30 parts of ethylene acrylic resin, 12 parts of polyvinyl butyral, 14 parts of polyisobutylene, 2 parts of dioctyl phthalate; The raw materials of the polyethylene layer include the following components in parts by mass: 100 parts of high-density polyethylene, 26 parts of composite kaolin, 6 parts of polyethylene wax, 2 parts of antioxidant 168; Preparation method of composite kaolin, comprising the following steps: A1. Add kaolin and wollastonite into water (the mass ratio of kaolin to wollastonite is 10:3, and the mass-volume ratio of kaolin to water is 1 g:11 mL), mix evenly to obtain a mixed solution; A2. Add nitric acid with a concentration of 2 mol / L to the mixed solution to adjust the pH to 3.5, then grind it for 4.5 h at 25 °C. Then add nitric acid with a concentration of 2 mol / L again to adjust the pH to 1.5, and grind it for 2.5 h at 70 °C. Filter, wash, and dry to obtain composite kaolin; A method for preparing a steel pipe for water supply, comprising the following steps: S1. Blend the raw materials of the fusion-bonded epoxy layer, extrude, and pulverize to obtain epoxy layer powder; S2. Fusibly bond the epoxy layer powder onto the outer surface of the steel pipe to obtain a fusion-bonded epoxy layer; S3. Blend the raw materials of the adhesive layer, extrude, and pulverize to obtain adhesive layer powder; Apply the adhesive layer powder onto the surface of the fusion-bonded epoxy layer to obtain an adhesive layer; S4. Mix and extrude the components of the polyethylene layer raw materials to obtain a polyethylene layer, lay the polyethylene layer on the adhesive layer, and apply pressure for compounding to obtain a steel pipe for water supply.

[0036] Example 4 The difference between this example and Example 3 is only that the mass ratio of kaolin to wollastonite in this example is 10:6.

[0037] Example 5 The difference between this example and Example 3 is only that the mass ratio of kaolin to wollastonite in this example is 10:4.

[0038] Example 6 The difference between this example and Example 3 is only that the mass ratio of kaolin to wollastonite in this example is 10:4.5.

[0039] Example 7 The difference between this example and Example 3 is only that the mass ratio of kaolin to wollastonite in this example is 10:5.

[0040] Example 8 The difference between this example and Example 6 is only that the composite kaolin in this example is replaced with an equal mass of functionalized composite kaolin; A method for preparing functionalized composite kaolin, comprising the following steps: Add composite kaolin to xylene (the mass-volume ratio of composite kaolin to xylene is 1 g:8 mL), mix evenly, add ethylene-methyl acrylate copolymer, and stir at a speed of 300 rpm for 3 h until the ethylene-methyl acrylate copolymer can be completely dissolved. Concentrate and dry to obtain functionalized composite kaolin; wherein, the mass ratio of composite kaolin to ethylene-methyl acrylate copolymer is 10:1.

[0041] Example 9 The difference between this embodiment and Embodiment 6 is only that the composite kaolin in this embodiment is replaced with an equal mass of functionalized composite kaolin; The preparation method of the functionalized composite kaolin includes the following steps: Add the composite kaolin into xylene (the mass-volume ratio of the composite kaolin to xylene is 1 g:7 mL), mix evenly, add ethylene-methyl acrylate copolymer, stir at a speed of 200 rpm for 4 h until the ethylene-methyl acrylate copolymer can be completely dissolved, concentrate, and dry to obtain the functionalized composite kaolin; wherein, the mass ratio of the composite kaolin to the ethylene-methyl acrylate copolymer is 10:0.5.

[0042] Comparative Example 1 The difference between this comparative example and Embodiment 3 is only that the composite kaolin in this comparative example is replaced with an equal mass of kaolin.

[0043] Experimental Example 1 Test the impact strength of the polyethylene layers of the water supply steel pipes prepared in Examples 1 to 7 and Comparative Example 1 according to the method specified in GB / T 1843-2008 "Determination of Plastics - Izod Impact Strength", with the notch being Type A. Then, after ultraviolet treatment of the samples according to the method in GB / T 16585-1996 "Vulcanized Rubber - Artificial Weathering (Fluorescent Ultraviolet Lamp) Test Method", test the impact strength again. The ultraviolet conditions are: 0.89 W / m 2 , the temperature is 50 °C, the time is 480 h, the cycle time is 4 h, the ultraviolet light exposure time is 4 h for condensation, the sample size is 80 mm × 10 mm, and the thickness is 4 mm. The test results are shown in Table 1.

[0044] Table 1 Test Results of Impact Strength

[0045] As can be seen from Table 1, the decrease in the impact strength of the polyethylene layers of the water supply steel pipes prepared in Examples 1 to 7 of the present invention after ultraviolet treatment is smaller than that of Comparative Example 1. Therefore, in the present invention, the use of silica-coated kaolin improves the ultraviolet aging resistance of the water supply steel pipes.

[0046] Experimental Example 2 Test the impact strength of the polyethylene layers of the water supply steel pipes prepared in Example 6 and Examples 8 to 9 according to the method specified in GB / T 1843-2008 "Determination of Plastics - Izod Impact Strength", with the notch being Type A, and the sample size being 80 mm × 10 mm and the thickness being 4 mm. The test results are shown in Table 2.

[0047] Table 2 Test Results of Impact Strength

[0048] As can be seen from Table 2, the impact strength of the steel pipes for water supply prepared in Examples 8-9 of the present invention reached 70.9 kJ / m 2 or above. Therefore, in the present invention, the use of ethylene-methacrylic acid copolymer to treat composite kaolin improves the impact strength of the steel pipes for water supply.

[0049] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A steel pipe for water supply, characterized in that: It comprises a steel pipe and an anti-corrosion layer arranged on the outer surface of the steel pipe, wherein the anti-corrosion layer comprises a fused epoxy layer, an adhesive layer, and a polyethylene layer arranged in sequence from the inside to the outside; The raw materials of the polyethylene layer include the following components in parts by weight: 90-110 parts of high-density polyethylene, 24-30 parts of composite kaolin, 4-8 parts of lubricant, 1-3 parts of antioxidant; The preparation method of the composite kaolin comprises the following steps: A1. Add kaolin and wollastonite into water and mix well to obtain a mixed solution A; A2, adding acid to the mixed solution A to adjust the pH to 3-4, and sand grinding to obtain a mixed solution B; A3, adding acid to the mixed solution B to adjust the pH to 1-2, sand milling, filtering, washing, and drying to obtain the composite kaolin.

2. A steel pipe for water supply according to claim 1, characterized in that: The mass ratio of kaolin to wollastonite is 10:4-5.

3. A steel pipe for water supply according to claim 1, characterized in that: In step A2, the sand grinding is performed at a temperature of 20-30° C. and a time of 4-5 h.

4. A steel pipe for water supply according to claim 1, characterized in that: In step A3, during the sand grinding, the temperature is 60-80° C. and the time is 2-3 hours.

5. A steel pipe for water supply according to claim 1, characterized in that: In steps A2 and A3, the acid is independently hydrochloric acid or nitric acid.

6. A steel pipe for water supply according to any one of claims 1 to 5, characterized in that: The composite kaolin is functionalized composite kaolin; The raw materials of the functionalized composite kaolin include composite kaolin and ethylene-methacrylic acid copolymer in a mass ratio of 10:0.5-1.

7. A steel pipe for water supply according to claim 6, characterized in that: The method for preparing the functionalized composite kaolin comprises the following steps: The composite kaolin is added into xylene and mixed evenly, and ethylene-methyl acrylic acid copolymer is added, stirred, concentrated and dried to obtain the functionalized composite kaolin.

8. A steel pipe for water supply according to claim 7, characterized in that: The stirring time is 3-4 hours and the rotation speed is 200-300 rpm.

9. A steel pipe for water supply according to claim 1, characterized in that: The lubricant includes one or more of zinc stearate, calcium stearate, and polyethylene wax; The antioxidant includes one or more of antioxidant 126 , antioxidant 1076 , and antioxidant 168 .

10. A method for preparing a steel pipe for water supply, used for preparing a steel pipe for water supply as claimed in any one of claims 1 to 9, characterized in that: The following steps are involved: S1, blending, extruding, and crushing the raw materials of the sintered epoxy layer to obtain epoxy layer powder; S2, sintering the epoxy layer powder onto the outer surface of the steel pipe to obtain a sintered epoxy layer; S3, blending, extruding, and crushing the raw materials of the adhesive layer to obtain an adhesive layer powder; applying the adhesive layer powder on the surface of the fused epoxy layer to obtain an adhesive layer; S4. Mix and extrude the components of the polyethylene layer raw material to obtain a polyethylene layer, lay the polyethylene layer on the adhesive layer, press and laminate, and obtain the steel pipe for water supply.

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